The present invention relates to a storage capacitor power supply which stores electrical power in a capacitor block consisting of a plurality of electric double layer capacitors connected in series, in parallel or in any combination of series and parallel and supplies electrical power to a load.
Discussions have existed for many years as to whether exhaust gas from automobiles with gasoline engines should be controlled because of problems with the global environment. In practice, the annual production of automobiles is still on the upswing but there is no prospect of reduction in automobile emissions. Under these circumstances, electric vehicles with batteries or solar cells have attracted attention as vehicles producing no exhaust gas. Therefore, there is an urgent need of early realization of practical electric vehicles.
In recent years, electric vehicles have begun to be used as vehicles in business applications such as urban-delivery vehicles and garbage trucks which are not required to travel a long distance continuously or to run at high speeds. Vehicles running at high speeds faster than 100 km/h and traveling about 200 km continuously have been reported as experimental vehicles. Furthermore, vehicles which have solar cells on the top of the body and run while charging the cells have been proposed. In addition, hybrid vehicles driven by both an internal combustion engine and an electric motor have been proposed.
One promising type of electric vehicle is a vehicle which has no gearing as used in an automobile with an internal combustion engine but drives the four wheels independently, using wheel motors. The driving mechanism of this vehicle is simplified. Also, the problems with the operating characteristics and the operability can be solved by coordinating and controlling the wheel motors. The greatest technical problem with the electric vehicle is to realize an ideal power source, i.e., a battery having a capacity comparable to an automotive engine. In order to put the electric vehicle into practical use, a battery is needed which is comparable in size and weight to an internal combustion engine and whose capacity can deliver power comparable to the power delivered by a gasoline engine. Furthermore, the battery must be recharged quickly or must be replaced with a fully charged battery as simply as a supply of gasoline.
However, no conventional battery can satisfy the above-described requirements. One especially great problem is that it takes long for the prior art battery to be recharged. In spite of this fact, the prior art battery is larger in size and heavier than the internal combustion engine.
An electric double layer capacitor which is smaller in size but larger in capacitance than the prior art capacitor has been developed. This electric double layer capacitor tends to be used to back up a power supply or for other application. When a large-capacity capacitor such as this electric double layer capacitor is employed as a storage capacitor power supply, it has advantages in being lighter and having longer life than a lead-acid battery and other batteries. However, if the voltage applied to the electric double layer capacitor exceeds the rated voltage, then the capacitance of the capacitor is immediately reduced. Also, the leakage current increases. In this way, the capacitor is adversely affected. Another disadvantage is that the internal resistance and the maximum working voltage are not sufficiently controlled. For these reasons, positive use of the electric double layer capacitor for power use is not yet made.
Heretofore, when a secondary battery is recharged, various difficulties have arisen in precisely detecting the completion of the recharging or knowing how much electricity can still be obtained from the battery.
Various contrivances have been made to detect the completion of the recharging. One method is to set the end voltage at a given voltage. Another method is to estimate the completion from the amount of electricity flowed into the battery. A further method is to detect the instant at which the voltage slightly drops due to the temperature characteristics of the battery after it is recharged for a given time. In spite of these contrivances, the recharging characteristics vary widely according to the conditions of the battery, i.e., depending on whether the battery is new or old, on the extent to which the battery ages, on the recharging current, and on whether the battery has been used continuously or was recharged.
Also, various contrivances have been made to measure the remaining electric power. One method is to measure the terminal voltage while applying a given load. Another method is to calculate the amount from the amount of electricity charged and discharged. A further method is to estimate the amount from the temperature and the specific gravity of the electrolyte. However, the battery characteristics vary widely, depending on the performance of each individual battery, on whether the battery is new or old, on the history of the use of the battery, on the load, on the conditions imposed when the recharging is made, and on other factors.
As described above, it can be said that hardly any method of precisely detecting the full charge point at all times is available. Also, hardly any method of detecting the amount of the residual electric power in the battery exists. Furthermore, to make effective use of the electric power of the battery, it is customary to overcharge it to a given level. Also, it is essential to know the amount of the electricity remaining in the battery. In the future, electric vehicles will be put into practical use, and secondary batteries will be used routinely. Under these conditions, the wasteful consumption of electrical energy due to overcharge will present a problem that cannot be neglected. We may expect that the practicability of the battery depends on whether it is possible to know the distance that the vehicle can still travel.
It is an object of the present invention to provide a long-lived, lightweight storage capacitor power supply which is capable of being quickly charged and of supplying a regulated voltage to a load.
It is another object of the invention to provide a storage capacitor power supply which stores electricity efficiently by the use of capacitors and supplies electric power to a load.
It is a further object of the invention to provide a storage capacitor power supply which permits precise detection of full charge point, thus preventing wasteful overcharge and undercharge.
It is yet another object of the invention to provide a storage capacitor power supply which makes it possible to precisely measure the amount of remaining electricity and to reliably know the limit of the operation.
These objects are achieved in accordance with the teachings of the invention by a storage capacitor power supply adapted to store electricity in a capacitor block consisting of a plurality of capacitors connected in series, in parallel or in any combination of series and parallel and to supply electric power to a load, said power supply comprising: the capacitor block connected with the load and supplying electric power directly to the load; a charging circuit for electrically charging the capacitor block; a charging power supply connected with the capacitor block via the charging circuit; and charge-limiting circuits which detect the voltages developed across the capacitors and limit charging of the capacitors if the detected voltages reach a given value.
One embodiment of the invention further includes charge-limiting circuits and full charge-detecting circuits connected in parallel with their respective capacitors. The charge-limiting circuits cause the charging current to bypass the capacitors. The full charge-detecting circuits sense that the charge-limiting circuits are operated and make a decision to see that full charge is attained. In another embodiment, the power supply further includes a residual electricity-detecting circuit. This residual electricity-detecting circuit consists of a multiplier and an arithmetic circuit. The multiplier takes the voltage developed across the capacitor and produces the square of the taken voltage. The arithmetic circuit multiplies the voltage by a constant factor. In a further embodiment, the residual electricity-detecting circuit takes the voltage developed across the terminals of the capacitor, applies the voltage to a series combination of a resistor, a voltage regulation element, and a detecting device, and detects a current according to the residual electricity by means of the detecting device.
The invention further offers a storage capacitor power supply for supplying electric power to a load from charged capacitors, said power supply comprising: a first capacitor block connected with the load and supplying electric power directly to the load; a charging circuit for electrically charging the first capacitor block; a second capacitor block connected with the first capacitor block via the charging circuit and acting as a power supply for the first capacitor block; and a charging control circuit which detects the voltage developed across the terminals of the first capacitor block and controls the charging circuit in such a way that the first capacitor block is charged by the second capacitor block until the detected voltage reaches a given voltage.
The novel storage capacitor power supply comprises the capacitor block connected with the load and supplying electric power directly to the load, the charging circuit electrically charging the capacitor block, and the charging power supply connected with the capacitor block via the charging circuit. The voltage developed across the terminals of each capacitor is detected. The charge-limiting circuit senses that this voltage has reached a given value and limits charging of the capacitor. Therefore, the capacitor block can be used up to the intended maximum voltage. Hence, the efficiency at which the electrical energy is stored can be enhanced.
Other objects and features of the invention will appear in the course of the description thereof which follows.